1. Field of the Invention
The present invention relates to a throttle valve opening control device, and more particularly to a throttle valve opening control device and the related layout structure within a motorcycle.
2. Description of the Background Art
Applicant has determined that the background art suffers from the following disadvantages. A throttle valve opening control device has been available for controlling openings of throttle valves using a drive motor, e.g., see Japanese Unexamined Patent Publication 2002-256900 (specifically pages 3 to 6; FIG. 9; and FIG. 10 of this document). FIG. 9 of this patent document is discussed hereinafter in conjunction with accompanying FIG. 7 of the present application, and FIG. 10 of this patent document is discussed in conjunction with FIG. 8 of the present application. However, as discussed in greater detail hereinafter, FIGS. 7 and 8 of the present application have been renumbered with different symbols.
FIG. 7 is a cross-sectional view showing a conventional throttle valve opening control device of the background art. As shown in FIG. 7, a front-side throttle body 302 is mounted on a front-side cylinder head 301 of a V-shaped engine, an intake passage 303 is formed in the front-side throttle body 302, a valve shaft 304 penetrates the intake passage 303, and a throttle valve 306 is mounted on the valve shaft 304. In the same manner, a rear-side throttle body 312 is mounted on a rear-side cylinder head 311, an intake passage 313 is formed in the rear-side throttle body 312, a valve shaft 314 penetrates the intake passage 313, and a throttle valve 316 is mounted on the valve shaft 314. A drive motor 317 that drives these throttle valves 306, 316 is arranged between the front-side throttle body 302 and the rear-side throttle body 312, e.g., between the throttle valves 306, 316.
FIG. 8 is a plan view showing the conventional throttle valve opening control device of the background art. FIG. 8 shows that the drive motor 317 is connected to the valve shaft 314 by way of a gear case 321 and, at the same time, the valve shaft 304 is connected to the valve shaft 314 by way of a link mechanism 322. By driving the valve shafts 304, 314 using the drive motor 317 as shown, the throttle valves 306, 316 can be opened and closed.
In mounting an engine on a vehicle body, particularly with respect to a motorcycle, a reduction in size of the engine is vitally important for the overall reduction of the space required for mounting the engine. The above-mentioned drive motor 317 shown in FIG. 7 and FIG. 8 is arranged between the front-side throttle body 302 and the rear-side throttle body 312. Accordingly, the present inventor has determined that it is difficult to further decrease a distance between the front-side throttle body 302 and the rear-side throttle body 312, e.g., as an attempt to miniaturize the engine. The present inventor has also determined if the front-side throttle body 302 and the rear-side throttle body 312 can be arranged closer to each other, an upper portion of the engine can be made more compact, and the engine can therefore be made smaller. In addition, by taking the layout and structure of the throttle valve opening control device into consideration, the further the engine's size can be reduced.